#include <iostream>
#include <fstream>
using namespace std;
int deq[5000002], v[5000002];
ifstream in("deque.in");
ofstream out("deque.out");


int main()
{
    int bk = 0, ft = 0, n, k;
    long long s = 0;
    in>>n>>k;
    for(int i = 1; i<=n; i++)
        in>>v[i];
    for(int i = 1; i<=n; i++)
    {
        while(v[i] <= v[deq[bk]] && bk >= ft)
            bk--;///eliminam elemente din spatele cozii dc sunt mai mari decat a[i]
        bk++;
        deq[bk] = i;

        if(deq[ft] == i-k)
            ft++;
        if(i>=k)
            s+=v[deq[ft]]; /// min e in varful cozii
    }
    out<<s;
    return 0;
}